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New Tools for Terrain Gravimetry

Periodic Reporting for period 2 - NEWTON-g (New Tools for Terrain Gravimetry)

Reporting period: 2019-06-01 to 2020-11-30

Gravimetry is a powerful geophysical tool, able to address issues that cannot be solved by other techniques. By studying the changes in gravity at the ground surface, one can obtain unique information on changes in subsurface mass, that may reflect processes involving subsurface fluids.
Gravimetry can thus play an important role in many contexts, including management of resources (water, hydrothermal fluids, hydrocarbons) and mitigation of natural hazards (e.g. volcanic activity).
The main reason why gravimetry is still a largely underexploited technique is related to the characteristics of available gravimeters that are very expensive and not well suited for continuous measurements in out-of-the-lab conditions. On average, the cost of a relative gravimeter is more than an order of magnitude higher than the cost of a seismometer or a GPS receiver, which explains why dense networks of the latter instruments have been deployed to study several geodynamically active areas, while no research institution or monitoring agency can afford the installation of more than 2-3 continuously running gravimeters in a single area. Furthermore, currently available instruments to perform continuous gravity measurements require facilities that are difficult to achieve in remote areas.
NEWTON-g proposes a radical change of paradigm for gravimetry. The project aims at developing a field-compatible gravity imager (Fig. 1), able to real-time monitor the evolution of subsurface mass changes. This system includes an array of low-costs MEMS relative gravimeters, anchored on an absolute quantum gravimeter; it is meant to provide imaging of gravity changes with unparalleled spatio-temporal resolution.
The relatively low-cost of the MEMS devices will democratize the gravimeter industry by making the necessary technology affordable, thus vastly increasing the number of potential users.
During years 3 and 4 of NEWTON-g, the gravity imager will be field-tested at Etna volcano (Italy), where data from the new devices will be validated against data provided by standard instruments in the permanent monitoring system. Specific studies will be carried out, aimed at developing strategies to best incorporate the new information from the gravity imager within other relevant datasets, so that it is best used to forecast changes in the state of activity.
During RP1 (year 1; “Design” phase), the activity concerned (a) the definition of the requirements for the new gravimeters (D4.1); (b) the definition of the design strategies aimed at fulfilling those requirements (D2.1); (c) the development of a numerical algorithm aimed at optimizing the configuration of the devices in the gravity imager; (d) the definition of the strategy for archiving and distributing the project’s data (D3.1).
The general rules for accessing NEWTON-g’s data and issues concerning the availability, exchange, use and maintenance of the data were discussed in D1.1 while detailed implementation of the principles set out in D1.1 was addressed in D1.2 which describes the nature of the data and the strategies to make them compliant with the FAIR principles.
During RP1 the project logo was also released and the NEWTON-g website was launched (D5.1). Dissemination activities also involved: (i) the organization of the kick-off workshop of NEWTON-g (D5.2); (ii) the release of the project’s dissemination and exploitation plan (D5.3); (iii) the production of a project video (D5.4).

During RP2 (month 13 to 30; “Production” phase and beginning of the “Field deployment and data utilization” phase), the activity concerned (a) the validation of the design of MEMS (D2.2) and quantum (D2.3) gravimeters; (b) the preparation of the plan for the deployment of the gravity imager at Mt. Etna (D3.2); (c) the production of the first prototypes of MEMS and quantum devices and the validation of their performances (D2.4 and D2.5); the design and development of the field infrastructures (D3.3); the development of software tools to handle and interpret the data produced by the gravity imager (D4.2 and D4.3); the deployment of the new measurement system at Mt. Etna (D3.4).
The breakout of the COVID-19 pandemic severely affected the project implementation as of March 2020 (month 22). Indeed, the enforced lockdown measures prevented the UNIGLA-IGR team from obtaining a field prototype of the MEMS gravimeter ready for installation at Mt. Etna in the summer of 2020. As a consequence, only the quantum gravimeter was installed at Mt. Etna in 2020 (late July) and the deployment of the gravity imager will be completed, with the installation of the MEMS pixels, one year later than planned (summer of 2021).
During RP2, a paper focused on the rationale and objectives of NEWTON-g was published in a peer-reviewed journal (Carbone et al., 2020. Front. Earth Sci. 8:573396).
Progress beyond the state of the art
The core objective of the NEWTON-g consists in advancing the hardware for gravity measurements beyond the current state-of-the-art.
NEWTON-g aims at developing the world’s first field versions of MEMS relative and quantum absolute gravimeters. We have already validated the design of both devices, thus setting the first stepping-stone beyond the state-of-the-art.
Another important objective of NEWTON-g involves the development of the gravity imager and its deployment at Etna, where its performances will be validated against standard instrumentation in the monitoring system of the volcano. The achievement of this objective will lead to a paradigm shift in gravimetry. The design of the gravity imager has also been validated during the first reporting period of NEWTON-g, which makes another important advancement beyond the state-of-the-art.

Expected results until the end of the project
By the end of the project we expect to demonstrate that the newly developed MEMS and quantum gravimeters can operate under harsh field conditions and measure the gravity acceleration to a suitable level of precision. NEWTON-g will drive the development of a new generation of gravimeters and the field-test at Etna will foster the application of the new sensors also in domains other than volcanology, including hydrology, geodynamics, reservoir monitoring, oil, gas and mineral prospecting.
Furthermore, we aim to demonstrate the potential of the gravity imager. It will be the first time an array of several continuously recording gravimeters is deployed in a single area, allowing imaging of sub-surface fluid dynamics to be achieved with unprecedented time and space resolution. The final validation of the gravity imager will be the real-time direct observation of volcano-related gravity changes through an extended array of gravimeters, a world’s first!

Potential impacts
We expect that the development of the new gravimeters will broaden the use of gravimetry, making it much more popular.
Once the capabilities of the gravity imager are demonstrated, we expect that the new gravimeters will be deployed as an array of continuously running devices at other volcanoes worldwide. NEWTON-g will thus help to take a step forward in volcano monitoring, through opening a new window for hazard assessment.
We also expect that the methodology and workflow of NEWTON-g will be applied to domains other than volcanology. For example, reservoir monitoring (water, oil or gas) could benefit from the results obtained within NEWTON-g, towards a more sustainable management of underground resources.
"The ""gravity imager"" includes an array of MEMS gravimeters, anchored to a quantum gravimeter."
Logo of NEWTON-g